Resource Scheduling in a Cellular System

ABSTRACT

The invention relates to a method for scheduling resources for uplink transmissions in a radio access network comprising access points which own pre-assigned resources. The invention also relates to an access point ( 5 - 7 ), a user terminal ( 1 - 4 ) and an access point controller  8 . Characteristic features of the invention are that each AP places its resources to the disposition of other APs in the access network, and that an AP ( 7 ) transmits a blocking signal (BLOCK R 3 ) if it does not allow a UT ( 3 ), which is served by an AP ( 5 ) in another cell, to use its resources (R 3 ). A UT that detects a blocking signal from an AP that owns the resources on which the UT is transmitting immediately stops transmission on said resources. The signal quality of a detected blocking signal may be used for setting the transmission power on the resources the UT has borrowed from the AP which transmits the blocking signal. Based on statistics on the APs which transmit blocking signals long-term pre-allocation of resources among the APs is made.

The invention relates to a method for scheduling radio resources inuplink transmissions in a cellular system. The invention also relates toa user terminal (UT), an access point (AP) and an access pointcontroller (APC) adapted for use of the method.

TECHNICAL BACK GROUND

A cellular system has a limited amount of radio resources in formfrequency bands, time slots, orthogonal codes and combinations thereof.A cellular system comprises a plurality of access points (APs), terminalunits (TUs) and one or a few access point controllers (APCs).

In cellular systems it is crucial to somehow control of use of the radioresources. A radio communication link between a transmitter and areceiver is typically disturbing several other radio communication linksthat are occurring simultaneously in the system. Radio resourcemanagement (RRM) algorithms designed to address this problem typicallybelong to two fundamentally different categories: Centralized RRMmethods and distributed RRM methods. Either the RRM method relies onhaving a central node (e.g. the APC) controlling how all the other nodesin the system (e.g. the APs and the UTs) use the radio resources, or thedifferent nodes are given authority to make decisions them self on whatradio resources to use. It is common when designing a cellular system torely on both centralized and distributed RRM methods. Some decisionsregarding the use of radio resources are taken by the central controllerand other decisions may be taken by the other nodes in the system. Theremay also be a hierarchy of RRM nodes, e.g. an APC may delegate some RRMdecisions to the APs and/or the UTs.

RRM methods may also be categorized into static versus dynamic RRMmethods. In a static RRM method the available radio resources is dividedinto a plurality of separate resources and each node is allocated asubset of these resources on a static basis [ref. 1]. One example of astatic RRM method is to deploy the system with a frequency re-use factorso that not all radio frequencies are allowed in every cell.

A problem with a static division of radio resources is that the loadsituation may be very different in the different cells. While one cellis heavily loaded and in the need of more resources the neighbouringcell might have unused resources left. System resources are not usesefficiently.

Dynamic RRM methods, on the other hand, constantly try to optimize andre-allocate the usage of the radio resources based on different types ofinformation e.g. interference measurements and/or traffic load [ref. 2].Nevertheless, the RRM decisions can be made in both centralized anddecentralized ways.

In a cellular system the uplink and the downlink are fundamentallydifferent in many ways and hence the RRM methods to be used in theuplink and downlink must be designed accordingly.

One important difference is that in the uplink the data to betransmitted is generated in the UT and a central RRM node will typicallynot know when a UT needs to transmit, or how much data it needs totransmit. Without this knowledge it is difficult for a centralized RRMmethod to make efficient decisions about the use of the radio resources.Typically for the uplink the UTs must inform the central node that itwants to transmit, and then the central RRM node (e.g. the APC) mustprocess this information and make a decision which it then informs theUT about. This is typically a rather slow process, which causes delaysin the system and the required signalling consumes radio resources,resulting in a degraded system performance. Hence, it would be desirableto find means for more efficient RRM methods.

Another fundamental difference between the uplink and the downlink isthat the downlink signals directed to all different UTs are (typically)transmitted from the same physical location, i.e. the AP antenna. Henceeach UT receives a signal consisting of a superposition of signalsdirected to all UTs that are affected by the channel from the AP to thecorresponding UT. From the perspective of a single UT all downlinksignals have passed trough the same radio channel. Hence, the relativepower ratios between signals directed to different UTs are maintained inthe downlink. In the uplink on the other hand, each UT transmitter is(typically) located in different physical positions and hence the APreceives a superposition of signals from the different UTs that havepassed through different radio channels. An efficient RRM method for theuplink should be able to take advantage of this fact in some way. In[ref. 3] an automatic frequency allocation (AFA) algorithm is disclosed.AFA is intended for solving the problem of allocating channels (i.e.radio resources) to different APs. AFA is using a Hiperlan/2 (highperformance radio local-area network, type 2) protocol that provideswireless multimedia communications between UTs and various broadbandcore networks.

DESCRIPTION OF THE INVENTION

The invention only applies to the uplink of a cellular radio system. Thebasic idea of the invention is to assign physical resources to all theAPs but to also allow these resources to be shared between the APs in afast way. To comply with this the invention proposes that resourcespre-allocated to individual APs are treated as something that the APsalways lend out to UTs in other cells, unless they (the APs) explicitlysignal that they do not allow this. This is done as follows:

-   -   An AP that wants to inform UTs in other cells that it does not        allow them (the UTs in the other cells) to use the resources        pre-assigned to this AP transmits a blocking signal to inform        UTs in other cells about this (its desire not to lend out its        pre-assigned resources).    -   A UT that wants to be scheduled by an AP listens for any        blocking signals from other APs.    -   In its scheduling request the UT reports to the scheduling AP        the blocking signals it (the UT) can detect.    -   The scheduling AP will then schedule the UT either on the        resources owned (pre-assigned) to the scheduling AP or on        resources assigned to other APs for which the UT has reported        that it can not detect the corresponding blocking signals. A UT        that is scheduled to a resource not owned by the scheduling AP        must stop transmitting immediately if it detects the blocking        signal for the corresponding resource.

In the preferred embodiment of the invention the UT listens for blockingsignals, before it sends the scheduling request. In an alternativeembodiment the UT sends the scheduling request first and then listensfor any possible blocking signals.

When a blocking signal is detected by an UT the UT reports to itsserving AP the identity of the AP that is transmitting the blockingsignal. Different strategies may then be used for re-scheduling the UTon other system resources.

In an embodiment of the invention the signal quality with which a UThears a blocking signal is used by the UT for setting its transmissionpower. Preferably the transmission power is set inversely proportionalto the signal quality although any other suitable function which relatesthe signal quality to the transmission power may be used.

In a further embodiment of the invention the signal quality of thedetected blocking signals are reported to the APC and are used by theAPC either for long-term resource allocation between APs or for dynamicresource allocation between APs. If there is an AP that often transmitsblocking signals this indicates that the AP has too little resourcesallocated to it and that it should be granted more resources. Likewise,if there is an AP that seldom transmits blocking signals this indicatesthat the AP has too much radio resources allocated to it and that itshould be granted less resources. In other words the APC shallredistribute resources on the APs according to statistics on blockingsignals from individual APs.

These principles are applied in a method, an APC, an AP, and an UT, inaccordance with the accompanying claims. By applying the aboveprinciples fast and efficient re-allocation of resources for uplinktransmission is achieved.

Non-used resources at other APs are instantly available for use by an UTthat has data to transmit, or for use by an AP in a cell with hightraffic load. System resources are efficiently used in that unusedresources pre-allocated to a cell are put to the disposition of UTs inother cells.

The invention relies on the fact that if a UT can hear the downlinktransmission from an AP then it can also cause disturbance to that AP onthe uplink. UTs that cannot detect a blocking signal are typically notcausing any significant interference.

However if the uplink interference is not a problem to an AP then the APshould put its resources to the disposition of other cells and shouldnot transmit a blocking signal when it experiences the uplinkinterference.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general view of a cellular radio access network,

FIGS. 2-4 are diagrams illustrating the allocation of resources on theaccess points shown in FIG. 1,

FIG. 5 is a view similar to FIG. 1 illustrating resource scheduling inthe uplink in accordance with the present invention, at a certain timeinstant,

FIG. 6 is a view similar to FIG. 5 illustrating resource scheduling at acertain later time instant,

FIG. 7 is a view similar to FIG. 6 illustrating resource scheduling inthe uplink in accordance with the present invention, at a certain latertime instant,

FIG. 8 is a functional oriented block diagram of an AP in accordancewith the invention,

FIG. 9 is a functional oriented block diagram of a UT in accordance withthe invention, and

FIG. 10 is a functional oriented block diagram of an APC in accordancewith the invention.

In order to better understand the present invention an example ofpre-allocation of resources in accordance with common known technologyis first described with reference to FIG. 1.

FIG. 1 illustrates a cellular radio access network comprising threecells A, B and C, schematically shown as hexagons, user terminals 1-4,access points 5-7, an access point controller 8 and land lines 9.

This invention focuses on the uplink and it is assumed that a schedulerin each AP controls the uplink resources in each cell. It is furtherassumed that resource coordination between the cells is coordinated bythe APC. Each AP will be assigned a certain part of the overall radioresource that it will own and control. Typically the frequency domain isused to divide the radio resources between the APs and then each AP getsassigned a certain frequency range. Other means to divide the resourcesamong APs are also possible, e.g., in the time domain or code domain,although the frequency domain is used as an example in the following.

As shown in FIG. 2 the APC has allowed AP 5 in cell A to schedule userswith the power P_(max) in frequency band R1, and with the power P_(min)in the frequency bands R2 and R3. This allocation ensures some basicinterference separation between the cells and it allows each AP toschedule users within the cell using the pre-assigned resources.Likewise, as shown in FIG. 3, AP 6 in cell B is allowed to scheduleusers with the power P_(max) in frequency band R1, and with the powerP_(min) in the frequency bands R2 and R3. As shown in FIG. 4 AP 6 incell B is allowed to schedule users with the power P_(max) in frequencyband R1, and with the power P_(min) in the frequency bands R2 and R3.

An UT that wants to transmit data on a scheduled resource in the uplinkmust tell the AP that it has some data to transmit by sending ascheduling request (SR), typically on a contention based channel, e.g. arandom access channel (RACH), although periodic polling of the UTsstatus or other non-contention based methods could be envisioned. The APwill then reply with a scheduling grant (SG) message that includesinformation about what physical resources the UT should use.

A contention based channel is a channel adapted for transmission of thedata the user intends to transmit. A session for transmission of largeamounts of data, for example a video clip, requires a channel with largeband width while a telephone call can take place on a channel havingless band with requirements.

The UT can also start to transmit data directly on a contention baseduplink channel if any such channel is available or on the RACH if thatis possible. In that case the UT must know that it is not usingresources that are pre-assigned to some other AP.

The problem with the static division of resources depicted in FIG. 2-4is that the load situation may be very different in the cells. While onecell is heavily loaded and in the need of more resources, theneighbouring cells might have unused resources left. To change thestatic resource allocation would involve informing the APC and waitingfor the APC to decide on moving resources from a lightly loaded cell toa heavily loaded cell. This can be a rather slow process compared to thescheduling decisions, which typically are taken in the APs. By lettingthe APs take the scheduling decisions scheduling becomes a quick processadapted to cope with the rapidly varying resource requirements.

PREFERRED EMBODIMENTS

Using the idea behind the invention and the points listed above refer toFIG. 4 and FIG. 5 we assume that UT 1 is at time T₁ communicating withAP 7 using all available uplink capacity R1, R2 and R3. AP 7, beingfully loaded, is therefore sending out a blocking signal BLOCK R3 toinform UTs in neighbouring cells that it is not allowed to borrowfrequency band R3 at the moment. Since none of the other APs transmitsany blocking signal and consequently UT 1 does not detect any blockingsignal all three resources R1, R2 and R3 are used by UT 1. Thissituation is depicted in FIG. 5.

At a later time T₂ user terminal UT3 wants to transmit data. It detectsthe blocking signal BLOCK R3 for R3 but not for R2 (since no suchblocking signal is transmitted). UT3 informs its AP5 in the schedulingrequest that it wants to communicate using the resources R1 and R2. Theresource R3, which is not used since the blocking signal R3 for thisresource is detected by UT3, is indicated by the white arrow R3 in FIG.6. The AP5 grants this request and since AP5 now uses all of itsresources, it also transmits a blocking signal BLOCK R1. At time T₂ wehave the situation depicted in FIG. 6.

User terminal UT1 is located far away from AP5 and it does not detectthe blocking signal for R1. Therefore UT1 continues to transmit onresource R1.

At an even later time T₃ user terminal 4 wants to transmit and itdetects both blocking signals for the resources R1 and R3. It informs AP6 that it wants to communicate on resource R2 and is granted this. Attime T₃ the transmission has started and AP 6 sends out a blockingsignal BLOCK R2 for resource R2. This blocking signal is detected by UT3 but not by UT 1. As a result UT3 stops using the resource R2 and UT1continues to transmit on resource R1.

Having explained the mechanisms for controlling scheduling andre-scheduling of radio resources in the uplink some strategies forre-scheduling on resources will now be explained.

An AP that schedules a UT to a resource it does not own must be preparedthat the UT may not be able to use this resource. If no transmission isreceived the AP can assume that the UT detected a blocking signal forthis resource and the AP should then preferably schedule the UT again onsome other resource. For example when UT3 in FIG. 7 detects the blockingsignal BLOCK R2 and stops using resource R2, AP5 detects this and thenAP5 may try to schedule UT3 on any of the resources owned by respectiveAPs in the four non-shown neighbouring cells to cell A, therebyexcluding resources belonging to the APs in cells A and B. Alternativelythe UT may have to send a new scheduling request to explicitly informthe scheduling AP that it is not allowed to use the correspondingresource any longer.

An AP thus detects the under-use of resources that the AP granted to theUT and based on information on this under-use the AP takes are-scheduling decision.

An alternative solution to the same problem is the following: All APscontinuously listens to scheduling requests from UTs within the cell andin other cells. A UT that wants to transmit data selects an AP and sendsa scheduling request indicating what resources it wants to use to thatAP. Other APs listen for the scheduling request. Those which can hearthe request and which does not want the requesting UT to use theirrespective resources transmit a blocking signal to the UT. Thescheduling AP schedules the UT to a suitable resource. If the UT isscheduled to a resource not owned by the scheduling AP it can only usethat resource if it does not receive any blocking signal from any otherAP.

An AP in the cell serving the UT that transmits a scheduling requestwill hear the request. Neighbouring cells will also hear this requestand will, if applicable, instantly transmit their respective blockingsignals. The serving cell will therefore take its grant decision withoutbeing aware of these blocking signals.

In the first preferred method previously described the UT listens forblocking signals before it sends the scheduling request and in thesecond method the UT sends the scheduling request first and then listensfor any possible blocking signals. The difference is minor.

A UT may include information about how well it can receive each of theblocking signals. This information relate to the signal quality, such asnoise figure, bit error rate and signal attenuation. If a UT hears ablocking signal strongly then it should avoid that resource, in theexample the given frequency band, all together. But if it can detect ablocking signal only weakly then it could use that resource withsomewhat reduced power. The transmission power to be used on resourcemay be a function of the signal quality of the corresponding blockingsignal for that resource. Setting the transmission power inverselyproportional to the signal quality of the received blocking signal isthe preferred solution. Instead of measuring the strength on theblocking signal only, the UT could perform a similar measure on anothersignal with known transmission power, e.g., a common pilot signal.

The following is an example of how an APC, having information on thepresence of blocking signals, can provide a long-term resourceallocation or a dynamic resource allocation between APs. Either an AP ora UT reports the presence of a blocking signal to the APC.

Start by allocating all resources to all APs. If an AP reports to theAPC that the UTs which it is scheduling often receive blocking signalsfrom other APs, the APC divides the resource for which blocking signalsoften are received between the involved APs. In this manner APs whichhave a high traffic load will be allocated more resources.

If an AP reports to the APC that resource collisions seldom occur, theAPC may decide to allocate less radio resources to that AP.

The functional oriented block diagram in FIG. 8 shows an AP inaccordance with the invention. Further to the conventional meanssymbolically illustrated by block 11, it comprises a scheduler 12 thathas one resource list 13 per UT. The scheduler has knowledge of eachresource allocated to a UT which the scheduler serves. In particular thescheduler knows weather a resource can be used or not. The schedulertakes scheduling decisions and forwards these decisions to a transmitter14 for transmission of grant decisions. A receiver 15 receivesscheduling requests from the UTs served by the AP. The AP has atransmitter 16 for transmission of blocking signals. A blocking signalis transmitted whenever the AP decides that it needs exclusive use ofthe radio resources that got pre-assigned to the AP. The decision onwhen to transmit the blocking signal may be based on the currentinterference situation on the associated radio resource or on thecurrent traffic load situation. There are means 17 for measuring theinterference on each resource R1-R3 in the system, for example the S/Nratio. The interference measuring means 17 is adapted to trigger thetransmission of a blocking signal when the AP detects that a UT in adifferent cell starts to use the resources of the AP when the AP itselfneeds to use the resources. Data signals transmitted from a UT on theuplink are received by the AP by a receiver 18. The data signals areforwarded to and subject to further processing by the conventional means11. The AP further comprises means 19A for detecting under-use of radioresources that the scheduler has allocated to an UT, and means 19B forre-scheduling of radio resources to an UT under-using its scheduledresources.

The AP also comprises an optional receiver 19 that listens for blockingsignals from other APs and forwards this information to the scheduler12.

The UT shown in FIG. 9 comprises a conventional transmitter 20 for datathat has been generated by a non-shown application. Further toconventional UT means not shown, the UT comprises a receiver 21 forreceiving blocking signals from other APs, for receiving of schedulinggrant decision signals, and for receiving information on the radioresources the UT is allowed to transmit on. The UT further comprisesmeans 21A for aborting the UT's transmission on radio resources on whichthe UT is scheduled upon detection of a blocking signal from an APowning these resources. Detection means 21B detect the signal quality ofa blocking signal or pilot tone transmitted by an AP. Based on thereported channel quality a control device 21C controls the UT'stransmission power setting for the resources associated with the APtransmitting a blocking signal. There is a device 21D that inserts, in ascheduling request, the identities of APs from which blocking signalsare received. The UT also comprises means 21E for triggering thetransceiver 23 to send a renewed scheduling request when the UT detectsa blocking signal transmitted from an AP owning the radio resource onwhich the AP is scheduled. There is a scheduling request device 22connected to a transmitter 23 for transmission of a scheduling requestto an AP. A data buffer 24 provides information on the number of dataunits the UT wants to transmit. This number is typically included in thescheduling request.

The UT must, in the first embodiment of the invention, also provideinformation to its serving AP about any blocking signals the UT candetect. In particular the UT must provide the identities of the APswhich transmit blocking signals. In FIG. 9 the APs in the network arelabelled AP1, - - - APn, n being an integer.

The APC shown in FIG. 10 is comprises a receiver 25 for receivinginformation relating to blocking signals and for providing statistics onthis received information. There is one receiver 25 per each AP in thenetwork. A device 26 for long-term pre-allocating of resources toindividual APs provides pre-allocation of resources on a long-term basisbased on blocking signal statistics from individual APs. The APC furtherincludes re-allocation means 26A for long term re-allocation of thepre-allocated radio resources among APs based on statistics relating toblocking signals transmitted from APs. As noted above an AP that oftentransmits a blocking signal may be allocated increased resources, whilean AP that seldom transmits blocking signals probably owns too much andtherefore shall have its resources reduced. Each of the APs controlledby the APC is communicated the result of the pre-allocations made by thedevice 26. The APC comprises one transmitter 27 per AP. An AP thatreceives information on its pre-assigned resources updates its resourcelists 13 accordingly.

It should be noted that the APC does not receive any “physical” blockingsignals. Blocking signals are detected and processed by the UTs andpossibly also by the APs. The UTs tells their serving AP about whichblocking signals they detect, the AP may also listen for blockingsignals and the APs may forward that information to the APC in some way.Processing, such as averaging, may be performed by the AP. There may bean optional device in the AP deciding whether the APC should be informedabout the statistics of the blocking signals or not. The reason toinform the APC about any blocking signals is to allow for re-allocationof the pre-assigned resource division between the APs.

-   [ref. 1] “Principles of Mobile Communication”, Gordon L Stüber,    Kluwer Academic Publishers, 1996, pp. 14.-   [ref. 2] “The performance of adaptive frequency allocation in an    environment on non-cooperative interference”, Johan Bergkwist and    Olav Queseth, S/3 Radio Communication Systems, KTH, Kista, Sweden,    available at    www.s3.kth.se/radio/Publication/Pub2004/OlavQueseth2004.-   [ref. 3] J. Huschke, G. Zimmermann: “Impact of Decentralized    Adaptive Frequency Allocation on the System Performance of    HIPERLAN/2”, Proceedings of IEEE Conference on Vehicular VTC'2000    Spring, vol. 2, pp 895-900, Tokyo, Japan.

1. A method for scheduling resources for uplink transmissions in a radioaccess network comprising a plurality of access points (AP) each oneowning pre-assigned resources, and user terminals (UT), including thesteps of characterized by each AP placing its resources (R1-R3) to thedisposition of other APs, each AP transmitting a blocking signal (BLOCK)if it does not allow other APs to use any of its resources, each UTlistening for blocking signals, and an AP serving a UT scheduling the UTon its own resources and/or on resources belonging to one or more otherAPs.
 2. A method in accordance with claim, characterized by a UTstopping its transmission on upon detection of a blocking signal from anAP owning a resource on which the UT is transmitting.
 3. A method inaccordance with claim 2, an UT wanting to transmit sending a schedulingrequest to an AP and including therein an indication of the amount ofdata to be transmitted, an AP in response to the request schedulingresources on the requesting UT, characterized by the AP wanting totransmit data including in the scheduling request information on APsfrom which it detects blocking signals.
 4. A method in accordance withclaim 3, characterized by each UT measuring a signal quality of theblocking signals it detects.
 5. A method in accordance with claim 4,characterized by including in the scheduling request a signal quality ofthe detected blocking signals.
 6. A method in accordance with claim 5,characterized by setting the transmission power on a resource, whichbelongs to an AP from which a blocking signal was detected, as afunction of the signal quality of the blocking signal so that the betterthe signal quality of a blocking signal is, the less is the transmissionpower.
 7. A method in accordance with claim 6, characterized by using asfunction an function that is inversely proportional to the signalquality.
 8. A method in accordance with claim 7, characterized by usingas function a quantised function.
 9. A method in accordance with claim3, characterized by a UT receiving blocking signals from one or more APsmeasuring the signal quality of a pilot tone transmitted from therespective APs from which blocking signals were received.
 10. A methodin accordance with claim 9, characterized by setting the transmissionpower on a resource, which belongs to an AP from which a blocking signalwas detected, as a function of the signal strength of the pilot tonetransmitted by that AP, so that the better the signal quality of thepilot tone, the less is the transmission power.
 11. A method inaccordance with claim 10, characterized by using as function an functionthat is inversely proportional to the signal quality.
 12. A method inaccordance with claim 8, characterized by using as function a quantisedfunction.
 13. A method in accordance with claim 3, characterized by anAP scheduled on resources that belong to one or more other APs listeningfor blocking signals before transmitting, sending a renewed schedulingrequest to its serving AP if it detects a blocking signal from one ofsaid one or more APs, and including in the request information on theblocking signals it currently detects.
 14. A method in accordance withclaim 3, characterized by an AP, not receiving transmission from a UT ona resource it scheduled on the UT, re-scheduling resources on the UT.15. A method in accordance with claim 14, characterized by the AP takingthe re-scheduled resources among APs from which no blocking signals weredetected by the UT, this time excluding said one or more APs.
 16. Amethod in accordance with claim 2, characterized by each AP listeningfor scheduling requests signals from the UTs, thereby gaininginformation on UTs that potentially may be scheduled on its resources,and each AP on basis of received scheduling requests taking a decisionto transmit a blocking signal.
 17. A method in accordance with claim 16,characterized by each UT measuring a signal quality of the blockingsignals it detects.
 18. A method in accordance with claim 17,characterized by a UT reporting to its serving AP the signal quality ofthe blocking signals it detects.
 19. A method in accordance with claim18, characterized by setting the transmission power on a resource, whichbelongs to an AP from which a blocking signal was detected, as afunction of the signal quality of the blocking signal so that the betterthe signal quality of a blocking signal is, the less is the transmissionpower.
 20. A method in accordance with claim 19, characterized by usingas function an function that is inversely proportional to the signalquality.
 21. A method in accordance with claim 20, characterized byusing as function a quantised function.
 22. A method in accordance withclaim 21, characterized by a UT receiving blocking signals from one ormore APs measuring the signal quality of a pilot tone transmitted fromthe respective APs from which blocking signals were received.
 23. Amethod in accordance with claim 22, characterized by setting thetransmission power on a resource, which belongs to an AP from which ablocking signal was detected, as a function of the signal strength ofthe pilot tone transmitted by that AP, so that the better the signalquality of the pilot tone, the less is the transmission power.
 24. Amethod in accordance with claim 23, characterized by using as functionan function that is inversely proportional to the signal quality.
 25. Amethod in accordance with claim 24, characterized by using as function aquantised function.
 26. A method in accordance with claim 25,characterized by an AP scheduled on resources that belong to one or moreother APs listening for blocking signals before transmitting, sending arenewed scheduling request to its serving AP if it detects a blockingsignal from one of said one or more APs, and including in the requestinformation on the blocking signals it currently detects.
 27. A methodin accordance with claim 26, characterized by an AP, not receivingtransmission from a UT on a resource it scheduled on the UT,re-scheduling resources on the UT.
 28. A method in accordance with claim27, characterized by the AP taking the re-scheduled resources among APsfrom which no blocking signals were detected by the UT, this timeexcluding said one or more APs.
 29. A method in accordance with claim 2,wherein the radio access network comprises an access point controller(APC) for pre-allocation of resources to each AP, an AP thereby owningits pre-allocated resources, characterized by reporting detectedblocking signals to the APC, the APC using this information as a basisfor long term resource allocation between APs.
 30. A method inaccordance with claim 29, characterized by the APC increasing thepre-allocated resources of an AP that often transmits blocking signals.31. A method in accordance with claim 29, characterized by the APCreducing the pre-allocated resources of an AP that seldom receivesblocking signals.
 32. An access point for use in a radio access networkcomprising a plurality of access points (AP), and user terminals (UT),each access point being provided with scheduling means (12) forscheduling UTs on resources, and receiving means (15) for receivingscheduling requests from APs wanting to send information, characterizedby means (16) for transmitting a blocking signal when the AP does notallow other APs to use any of its owned resources, and the schedulingmeans being adapted to schedule the requesting UT on the AP's ownresources and/or on resources belonging to one or more other APs.
 33. Anaccess point in accordance with claim 32, characterized by means (19A)for detecting under-use of resources scheduled on an UT, means (19B) forre-scheduling an UT under-using its scheduled resources.
 34. An accesspoint in accordance with claim 32, characterized by means (15) forextracting, from scheduling requests, information on APs that aretransmitting blocking signals.
 35. A user terminal for use in a radioaccess network, the UT being provided with transmission means forsending a scheduling request to an AP characterized by means (21) forlistening for blocking signals transmitted by APs, and means (21A) foraborting the UT's transmission on resources on which the UT arescheduled upon detection of a blocking signal from an AP owning theseresources.
 36. A user terminal in accordance with claim 35,characterized by detection means (21B) for detecting the signal qualityof a blocking signal or pilot tone transmitted by an AT, and controlmeans (21C) that based on the detected signal quality controls the UT'spower setting for the resources associated with the AP that istransmitting the blocking signal.
 37. A user terminal in accordance withclaim 36, characterized by means (21D) for including in a schedulingrequest the identities of APs from which blocking signals are detected.38. A user terminal in accordance with claim 37, characterized by means(21E) for triggering the transmission means to send a renewed schedulingrequest when the UT detects a blocking signal transmitted from an APowning a resource on which the AP is scheduled.
 39. An access pointcentral (APC) for use in a radio access network comprising a pluralityof access points (AP) and user terminals (UT), the APC comprisingallocation (26) means for pre-allocation of resources to each AP,characterized by re-allocation means (26A) for long term reallocation ofthe pre-allocated resources among APs based on statistics by whichblocking signals are transmitted by the APs.
 40. An access point centralin accordance with claim 39, characterized by the re-allocation meansbeing adapted to increase the pre-allocated resources to an AP thatoften transmits blocking signals.
 41. An access point central inaccordance with claim 4+, characterized by the re-allocation means beingadapted to decrease pre-allocated resources to APs that seldom receiveblocking signals.